Distortion compensation in ink jet recording

ABSTRACT

An ink jet type recording arrangement is available to write or print successive characters on a recording medium. Such recording arrangement has a writing head which is horizontally moved to successively write the characters. In case the writing head is manually operated to write successive characters, the moving velocity of the writing head varies time to time. The variation of the moving velocity of the head causes the character to be distorted. In order to compensate for the distortion of printing character, therefore, it is required to detect the moving velocity of the manual-operating head and to generate control voltage in response to the detected velocity. The control voltage generated is applied to the horizontal deflecting electrodes incorporated into the head to control the writing of the characters due to the ink jet.

[ 1 Aug. 29, 1972 DISTORTION COMPENSATION IN INK JET RECORDING 3,128,340 4/1964 Harmon .Q .178/18 Primary Examiner-Kathleen H. Claffy [72] Inventor: Toshio Kashio, 1660 Gakuennishi- Assistant Examiner Thomasw Brown Machl Kodmra'shl Tokyo Japan Attorney-Nelson H. Shapiro [22] Filed: Dec. 1, 1969 211 Appl. No.: 881,127 [57] ABSIRACT An ink jet type recording arrangement is available to write or print successive characters on a recording [301' Forelgn Apphcanon pno-my D medium Such recording arrangement has ,a writing Dec. 6, 1968 Japan ..43/89026 head which is horizontally moved m successively Write the characters. In case the writing head is manually 52 us. Cl ..178/30, 346/1 operated to write Successive characters, the moving 51] Int. Cl. ..G0ld 15/18 velocity of the writing heed varies time to time The [58] Field of Search ..l78/18, 19, 20, 23, 30; variation of the meving velocity of the head causes the 340/324 A; 346/], 75 character to be distorted. In order to compensate for the distortion of printing character, therefore, it is [56] References Cited required to detect the moving velocity of the manualoperating head and to generate control voltage in UNITED STATES PATENTS response to the detected tl:elocity. Ttgp gontrol voltlage generated is applied to e horizon eflecting e ec- PI'COU X trodes incorporated into the head to control the i "346/ ing of the characters due to the ink jet. 3:372:398 3/1968 Nairn et a1. ..340/324 AX 10 Claims, 6 Drawing Figures OUT SAW TOOTH OUT r REGISTER W GENERATOR OUTn I G|| Gl$ Gm 13 f COUNTER -11 l SP IO, I2

STA S STP R I miminwm I912 3.688.034

sum 2 or 3 (4 FIG. 2

F SAW TOOTH r REGISTER GENERATOR QUT ouT'n I Gu G|$"" Gm v r COUNTER SP 10 1 %f|2 STAG S STP RFF '1 FIG. 3

(0 )STA] I P' l- '2 {2 P3 I I (b)STP 1 (C)FF(IO) Ll (d) CPJULFLFLFUUUW DISTORTION COMPENSATION IN INK JET RECORDING The invention relates to the generation of distortioncompensating voltage, and more particularly to a method for generating control voltage for use in recording arrangements advantageously available as output devices of electronic computers.

There have been various types of recording arrangements effective to output devices for computers, one of which is ink jet type recording arrangements as a high speed recording device having less number of movable parts in which the ink is projected through one nozzle by the electrostatic force, electromagnetic force, ultrasonic wave force and so on and the fine particles of the ink are deflected horizontally and vertically, thereby printing characters.

ln the ink jet type writing or recording arrangement of the type described above, the emitter is moved horizontally in order to print a plurality of characters and the like in succession. Therefore, when the movement of the emitter is not compensated, the printed characters are distorted. There have been known methods and devices for eliminating the distortion of the printed characters in which a sawtooth waveform voltage having a predetermined slope or gradient corresponding to the velocity of the emitter of the ink jet type recording arrangement is applied to the horizontal deflecting electrodes thereof. One example is disclosed in U.S. Pat. No. 3,136,594 issued on June 9, 1964. In the above method, the emitter is assumed to be moved at a constant velocity, but in the case of a manually operating recording device, that is, in case that an emitter for an ink jet type writing or recording arrangement (including an ink jet nozzle, accelerating electrodes, deflecting electrodes, and other components required) is moved on the recording medium at an arbitrary velocity, the sawtooth waveform voltage corresponding to the velocity of the writing head which varies from time to time must be generated for each character to be recorded. Otherwise, when the emitter (which is referred to as writing head hereinafter in this specification) is manually moved over the recording medium at an arbitrary velocity, the recorded or printed characters are subject to distortions, because the sawtooth waveform voltage applied to the horizontal deflecting electrodes of the head is not a function of the velocity of the head. In other words, the sawtooth waveform voltage applied to the horizontal deflecting electrodes has a predetermined gradient and the direction of ink jet is independent of the moving velocity of the writing head, so that the direction of ink jet cannot be followed in accordance with the variation in velocity of the writing head. Therefore, the direction of the ink jet cannot be oriented adequately to a desired point on the recording medium so that the printed characters or the like are distorted. More specifically, when the writing head is moved at high speed while the voltage having a predetermined constant slope is applied to the horizontal deflecting electrodes, the trailing portion of the characters being recorded or printed is displaced toward the direction of movement of the writing head. On the other hand, when the writing head is moved at a relatively slow speed, the trailing portion of the characters being recorded or printed will be displaced in the direction opposite to that of the movement of the head.

Accordingly, one of the objects of the present invention is to generate distortion-compensating voltage as a function of the moving velocity of a writing head or emitter.

Another object of the present invention is to control sawtooth waveform voltage to be generated and applied to the horizontal deflecting electrodes for the next succeeding recording or printing period on the basis of a measured value of the moving velocity of the writing head.

A further object of the present invention is to provide a method for generating distortion-compensation voltage including a sawtooth generator adapted to generate a sawtooth waveform voltage having a variable gradient or slope corresponding to a measured value of the moving velocity of the writing head.

A still further object of the present invention is to generate distortion-compensating voltage which enables the direction of the ink jet to be directed to one point on the recording medium for a predetermined time irrespective of the variation of the moving velocity of the writing head, thereby eliminating the distortion of the printed characters.

According to one aspect of the present invention, the moving velocity of the writing head is measured and distortion-compensating voltage is generated as a function of the measured velocity to adequately orient the flow of ink jet, with the result that the distortion of the printed characters may be eliminated.

According to another aspect of the present invention, the velocity of the writing head moving at different speeds over a predetermined distance is measured and distortion-compensating voltage to be applied to the horizontal deflecting electrodes is generated during a predetermined time period as a function of the measured velocity so that the inter-digit spaces and digit spaces are not adversely affected.

According to a further aspect of the present invention, in order to permit the writing head to'write or print the characters successively while moving the writing head horizontally, the voltage applied to the deflecting electrodes is always so controlled as to have a gradient corresponding to the moving velocity of the writing head, thereby controlling ink jet in the horizontal direction. Thus, not only the printed characters are not adversely affected, but also the distortion of the printed characters may be eliminated.

According to another aspect of the present invention, a velocity measuring circuit incorporated in the distortion-compensating voltage generating apparatus in accordance with the present invention is so arranged as to count pulses generated during time interval between the appearance of the writing stop signal and the next succeeding writing start signal, the counted pulses are stored in a register; and the sawtooth generator is controlled in accordance with the content of the register.

According to another aspect of the present invention, the sawtooth generator which is controlled by the output of the velocity measuring circuit has a plurality of the time constant circuits each having a different time constant. One of the time constant circuits is selected in response to the output of the velocity measuring circuit so as to control the sawtooth waveform output voltage in conformity with the measured velocity.

According to another aspect of the present invention, the sawtooth generator is energized during a predetermined period between the writing start signal and the writing stop signal so as to generate distortioncompensating voltage which is applied to the horizontal deflecting electrodes in order to compensate for the distortion of the characters to be recorded.

According to another aspect of the present invention, the sawtooth waveform voltage generated as a function of the moving velocity of the writing head is applied to the horizontal deflecting electrodes so as to controlthe same, so that the ink jet can be pinpointed to one fixed point on the recording medium even when the moving velocity of the writing head is varied.

The above and other objects, aspects and advantages of the present invention will become more apparent from the following description of one illustrated embodiment thereof in conjunction with the accompanying drawing, in which;

FIGS. 1A, 1B and 1C are graph diagrams for explanation of the principle of the present invention;

FIG. 2 is a block diagram of one embodiment of a distortion-compensating voltage generating apparatus in accordance with the present invention;

FIG. 3 shows the waveforms appearing in various portions of the apparatus shown in FIG. 2; and

FIG. 4 is a circuit diagram illustrating the details of the distortion-compensating voltage generating apparatus shown in FIG. 2.

A writing head for use in the ink jet type recording arrangement generally comprises an ink jet nozzle, accelerating electrodes and horizontal and vertical deflecting electrodes and this is moved transversely with respect to a recording medium at a constant speed for writing. However, the writing head used for the present invention is operated by manually moving the writing head on the recording medium such as bills so that the speed of the writing head is not constant. The writing head varies in speed from line to line and time to time. Therefore the printed characters are distorted.

The present invention is based upon such observation that the speed of the writing head passing through An interdigit space between two adjacent characters is substantially constant. In accordance with the invention, the time required for passing through the interdigit space (a space between the preceding character and the succeeding character) is measured to generate a sawtooth waveform voltage whose slope is in proportion to the speed of the writing head but in inverse proportion to the time, thereby compensating for the distortion of the next succeeding character.

The principle of the distortion-compensating voltage generating apparatus in accordance with the present invention will be described with reference to FIGS. 1A, 1B and 1C.

. Referring to FIG. 1, there is shown a graphic diagram illustrating the relation between the distance X and the time T with the speed v,, v and v being a parameter. Clearly, within a given time t, the displacements are X X and X which are in proportion to the speed or velocity. When it is assumed that the emitter position moves in the direction indicated by the arrow from the original point and that the target to which the ejected ink is directed is point A, the deflection angles 0,, 0 and 0 well become larger in proportion to the velocity as shown in FIG. 1B. Thus it is seen that in order to compensate for these deflection angles 6,, 0, and 0 a sawtooth waveform voltage whose slope is proportional to the velocity in the given time t and which varies in time may be applied to the deflecting electrodes of the writing head.

FIG. 1C shows that examples of sawtooth waveform voltages having different gradients with the time being plotted on the abscissa and the voltage V being plotted on the ordinate. From FIG. 1C it is seen that when the sawtooth waveform voltage V, having the gradient 0, is generated and applied to the deflecting electrodes for the moving velocity v of the writing head, the distortion of the printing character may be compensated. In the similar manner, when the writing head moves at v or v;, the sawtooth waveform voltages V or V may be generated and applied to the deflecting electrodes to compensate for the distortion of the printing character.

From the foregoing, it is seen that in accordance with the present invention, the distortion-compensating voltage corresponding to the moving speed of the writing head is generated so as to compensate for the distortion of the printing character. This will be described in more detail with reference to FIG. 2 illustrating a block diagram of one embodiment of the distortion-compensating voltage generating apparatus for use with an ink jet type recording arrangement.

In FIG. 2, STA designates an input terminal to which is applied a signal representing the writing start position of each character and STP, an input terminal to which is applied a signal representing the writing stop position of each character. The STA terminal is connected through a lead wire to a novel manual writing head proposed by the same applicant, which is provided with a roller for measuring the displacement of the writing head so as to intermittently close and open a switching mechanism, thereby generating a signal representing the writing start position. Thus, when the manual writing head of the type described above is moved on the recording medium, a writing start signal indicating the writing of one character is applied from the writing head to the input terminal STA through the lead wire. A writing stop signal indicating the end of the writin g is generated and applied to the input terminal STP after a predetermined time delay from the generation of the writing start signal.

FIG. 3 shows the waveforms of the voltages at various points of the distortion-compensating voltage generating apparatus shown in FIG. 2. The writing start signal transmitted from the writing head is shown in FIG. 3-(a). FIG. 3-(b) shows the writing stop signal which is generated independently of the writing start signal a predetermined time after the generation thereof or which is delayed by a predetermined time through a suitable time delay means. From FIG. 3-(a), it is seen that the time interval t between a writing start signal P1 for the one character and the next writing start signal P for the next character is inversely proportional to the moving velocity of the writing head. When the velocity of the writing head varies, the time interval also varies as shown for example by t2 between the signals P2 and P However, since the printing or writing space for one character remains unchanged, a writing stop signal p appears at a predetermined time T0 after the writing start signal P In this case. the time intervals t 1 and so on between the adjacent writing start signals are equal to those t,, t, andso on between the adjacent writing stop signals respectively.

Referring back to FIG. 2 again, the input terminal STA is connected to the set signal input terminal S of a flip-flop and to each input terminal of each of AND gates G,, to G,,,. The input terminal'STP is connected to the reset signal input terminal R of the flip-flop 10 and to the reset signal input terminal of a pulse counter 11. The set output of the flip-flop I0 is connected to the input terminal i of the pulse counter 11, whereas the reset signal output terminal is connected to the input terminal of an AND gate 12 and to the input terminal I of a sawtooth generator 13. The input terminal C? of clock pulses is connected to the input terminal of the AND gate 12 and the output terminal of the AND gate 12 is connected to the shift pulse input terminal SP of the pulse counter 11. The output terminals of the respective stages of the counter 11 are connected to the input terminals of a register 14 trough the AND gates G,, to G,,,. The output terminals OUT,, OUT,, .....OUT, of the register 14 are connected to associated input terminals of the sawtooth generator 13.

In operation, the voltage that is applied to the deflecting electrodes of the writing head must be so controlled that the ink jet from the writing head is directed to a predetermined target position for a predetermined time irrespective of the variation in velocity of the writing head.

The mode of operation will be described with reference to FIG. 2. When the manual writing head of the type described above is started to move, the writing start signal P, shown in FIG. 3-(a) is applied to the terminal STA, so that the flip-flop 1-0 is set. The set output of the flip-flop 10 sets the pulse counter 11 to an initial value. The writing stop signal P, as shown in FIG. 3-(b) is applied to the input terminal STP at a predetermined time 1,, after the generation of the writing start signal P,, so that the flip-flop 10 is reset so that such high level reset output as shown in FIG. 3-(c) is derived from the reset output terminal of the flip-flop 10, The reset output of the flip-flop l0 and the clock pulses as shown in FIG. 3-(d) open the AND gate 12 so that the shift pul ses are transmitted to the counter ll,'thereby causing the counter 11 to start counting. When the manual writing head is further moved, the next writing start signal P, is transmitted from the writing head (not shown) after the time interval t, and is applied to the AND gates G,, to G,,, so that the content of the counter 11 is transferred to the register 14 and stored therein. The register 40 in turn energizes one of its output terminals OUT, to OUT, in response to the content stored therein so as to apply the input to the sawtooth generator 13. The sawtooth generator 13 is applied with the reset output of the flip-flop 10. When low level reset output is applied to the sawtooth generator 13, that is when the flip-flop 10 is set, the sawtooth generator 13 is energized so that the output sawtooth waveform voltage having a slope corresponding to the content of the register 14 is derived from the output OUT of the sawtooth generator. The practical circuit diagram of the block diagram shown in FIG. 2 is illustrated in FIG. 4. Same reference numerals and characters are used to designate same parts and the arrangements and func- .tion of the components which have been already described with reference to FIG. 2 will not be described again hereinafter. 4

In FIG. 4, when the writing start signal is applied, the AND gates G,, to G,,, are opened so that the content of the counter 11 is transferred into the register 14 which has been reset. In this case, it should be notedthat the manual writing head is arranged not to operate to write a character in the first writing start signal P,. Therefore,

the initial counter condition will not affect the writing.

flip-flop FF-S, n stages of flip-flops FF-l to FF-n. for.

counting and gates associated therewith. The writing stop signal is applied to the input terminal STP after a predetermined time t, from the setting of the flip-flop FF-S so that the flip-flop 10 is high level reset. Therefore the reset output and the clock pulses shown in FIG. 3-(d) open the AND gate 12, thereby transmitting the shift pulses to the counter 1 1. Then, the set signal of the flip-flop FF-S shifts the counter flip-flops one by one to the right, thereby counting the pulses. The flip flop in each of the stages transmits the set output to one of the gates G,, to 6,, when the flip-flop is set, but these AND gates are closed so that no input is applied to the register 14. The writing start signal is applied to the input terminal STA after the movement of the writ ing head so that the AND gates are opened. Assuming that the flip-flop FF-n in the counter 1 l is set when the writing start signal P, is applied, the readout AND gate 6,, is opened so that the counter content is transferred to the register 14. The register 14 is of parallel type and comprises n stages of flip-flops R-l to R-n. Since the gate G,, is assumed to be opened, the flip-flop R-n of the register 14 is set so that the content of the counter is transferred to this flip-flop. Simultaneously, the flipflop 10 is set and the reset output of the flip-flop 10 is rendered low level so that no shift pulse is transmitted to the counter 1 1, thereby stopping the operation of the counter. The outputs OUT, to OUT of the register 14 are connected to the inputs IN, to IN of the sawtooth generator 13 so that when the flip-flop R-n of the register 14 is set the signal is applied to the input IN, of the sawtooth generator 13, which, in the instant embodiment, comprises a modified Bootstrap circuit.

This bootstrap circuit may be well understood when the portion enclosed by the dotted line is regarded as a resistor. In other words the bootstrap circuit is provided with a plurality of time constant circuits R,C; R,C; R,,C the number of which corresponds to the number of inputs and to which are connected the inputs IN, to IN respectively through transistors Tr, to Tr,,. More specifically, the base electrode of the transistor Tr, is connected to the input IN, while the collector-emitter circuit thereof forms a part of the time constant circuit R,C. In the similar manner, the base electrodes of the transistors Tr, to Tr,, are connected to the inputs IN, to IN, respectively and the emitter-collector circuits of the transistors Tr, to Tr, form the parts of their respective time contact circuits R,C to R,,C respectively.

So far it has been assumed that the content of the counter 11 is stored in the register 14, that is the flipthat to an input transistor Tri of the Bootstrap circuit is applied the negative-going signal shown in FIG. 3-(c), whereby the input transistor Tri is driven into the nonconductive state. When the input transistor Tri is rendered non-conductive, the transistor Tr is driven into the conductive state by the input signal applied through the input IN so that the capacitor C is charged through a resistor R The charged voltage of the capacitor C is directly applied to the base electrode of an output transistor Tro of an emitter-follower connection, thereby driving the transistor Tro into the conductive state. When the charged voltage across the capacitor C is increased and thus the voltage applied to the base electrode of the output transistor Tro is increased, the transistor Tro is further driven into the conductive state so that the voltage across an emitter resistor Re may be derived as the output voltage from the output OUT. When the writing stop signal P is applied to the input terminal STP after the predetermined time t from the generation of the writing start signal P; by which the writing operation of the writing head has been initiated, the flip-flop is high level reset and the reset output is applied to the base electrode of the input transistor Tri of the bootstrap circuit 13 so that the transistor Tri is driven into the conductive state and the capacitor C is discharged. Therefore, the output transistor is driven into the non-conductive state so that no output voltage is derived. The sawtooth waveform output voltage derived from the Bootstrap circuit 13 is shown in FIG. 3-(e). The output voltage is applied to the horizontal deflecting electrodes in the writing head in a well known manner so that the direction of ink jet is controlled in response to the gradient of the distortion-compensating voltage, thereby permitting the writing without distortion. When the flip-flop 10 is reset, both of the counter 11 and the register 14 are reset for the next writing operation.

What is claimed is:

l. A method of compensating for distortion in an ink jet type writing means moved manually at varying speed relative to a recording medium and having ink jet deflection means to which voltages are applied for writing characters, which comprises the steps of measuring the velocity of movement of said writing means, generating a voltage having a potential gradient which varies as a function of the measured velocity, and applying the generated voltage to said deflection means to compensate for the distortion of the characters written by said writing means due to relative movement of the writing means sand the recording medium.

2. A method in accordance with claim 1, wherein said measuring step comprises counting a plurality of clock pulses during an interval proportional to the said velocity, storing the number counted, and varying said potential gradient in accordance with said number.

3. A method in accordance with claim 2, wherein said voltage is generated by means including a plurality of different time constant circuits, and the gradient is varied by selecting a time constant circuit operable in the generating means in accordance with the number of pulses counted.

4. Apparatus for compensating for distortion in an ink jet type writing means moved at varying speed relative to a record g medium upon which successive characters are writ en in accor ance with voltages applied to ink jet deflection means of the writing means, comprisingmeans for measuring the velocity of movement of said writing means during the interval between the end of the writing of one character and the beginning of the writing of the next character, means connected to said measuring means for generating a distortion-compensating voltage during the writing of said next character, the magnitude of which voltage varies as a function of the measured velocity, and means for applying the generated voltage to the deflection means.

5. Apparatus in accordance with claim 4, wherein said generating means includes means for producing a variable potential gradient as a function of the measured velocity. v

6. Apparatus in accordance with claim 5, wherein said measuring means comprises means for counting a number of clock pulses during said interval, means forstoring the number of pulses counted during the writing of said next character, and means for connecting said storing means to said generating means for varying said potential gradient in accordance with the number stored.

7. Apparatusin accordance with claim 6, wherein said generating means is a sawtooth generator having a plurality of different time constant circuits selected in accordance with the number stored in said storing to ink jet deflection means of said writing means, comprising variable potential gradient voltage generating means, means connected to said generating means for controlling the voltage gradient in response to signals synchronized with the starting and stopping of characters written by said writing means, and means for applying the generated voltage gradient to the deflection means.

9. Apparatus in accordance with claim 8, wherein said controlling means comprises means for measuring the time between successive signals corresponding to the stopping of the writing of one character and the starting of the writing of the next character and for varying the voltage gradient in accordance with the measured time.

10. Apparatus in accordance with claim 8, wherein said controlling means comprises means for measuring the velocity of said writing means between the writing of successive characters and for varying the voltage gradient in accordance with the measured velocity. 

1. A method of compensating for distortion in an ink jet type writing means moved manually at varying speed relative to a recording medium and having ink jet deflection means to which voltages are applied for writing characters, which comprises the steps of measuring the velocity of movement of said writing means, generating a voltage having a potential gradient which varies as a function of the measured velocity, and applying the generated voltage to said deflection means to compensate for the distortion of the characters written by said writing means due to relative movement of the writing means sand the recording medium.
 2. A method in accordance with claim 1, wherein said measuring step comprises counting a plurality of clock pulses during an interval proportional to the said velocity, storing the number counted, and varying said potential gradient in accordance with said number.
 3. A method in accordance with claim 2, wherein said voltage is generated by means including a plurality of different time constant circuits, and the gradient is varied by selecting a time constant circuit operable in the generating means in accordance with the number of pulses counted.
 4. Apparatus for compensating for distortion in an ink jet type writing means moved at varying speed relative to a recording medium upon which successive characters are written in accordance with voltages applied to ink jet deflection means of the writing means, comprising means for measuring the velocity of movement of said writing means during the interval between the end of the writing of one character and the beginning of the writing of the next character, means connected to said measuring means for generating a distortion-compensating voltage during the writing of said next character, the magnitude of which voltage varies as a function of the measured velocity, and means for applying the generated voltage to the deflection means.
 5. Apparatus in accordance with claim 4, wherein said generating means includes means for producing a variable potential gradient as a function of the measured velocity.
 6. Apparatus in accordance with claim 5, wherein said measuring means comprises means for counting a number of clock pulses during said interval, means for storing the number of pulses counted during the writing of said next character, and means for connecting said storing means to said generating means for varying said potential gradient in accordance with the number stored.
 7. Apparatus in accordance with claim 6, wherein said generating means is a sawtooth generator having a plurality of different time constant circuits selected in accordance with the number stored in Said storing means.
 8. Apparatus for compensating for distortion in an ink jet type writing means moved at varying speed with respect to a recording medium for writing successive characters thereon in accordance with voltages applied to ink jet deflection means of said writing means, comprising variable potential gradient voltage generating means, means connected to said generating means for controlling the voltage gradient in response to signals synchronized with the starting and stopping of characters written by said writing means, and means for applying the generated voltage gradient to the deflection means.
 9. Apparatus in accordance with claim 8, wherein said controlling means comprises means for measuring the time between successive signals corresponding to the stopping of the writing of one character and the starting of the writing of the next character and for varying the voltage gradient in accordance with the measured time.
 10. Apparatus in accordance with claim 8, wherein said controlling means comprises means for measuring the velocity of said writing means between the writing of successive characters and for varying the voltage gradient in accordance with the measured velocity. 